The horse's handler was sitting in the buggy near Pier 45 when the horse "seemed to spook for no reason" and flung the handler to the ground at about 6:30 p.m., San Francisco police Sgt. Lyn Tomioka said.The handler suffered life-threatening injuries and was transported to San Francisco General Hospital, according to Tomioka.

The horse ran loose for about 20 minutes, during which time it knocked down two bicyclists before the animal was captured near Pier 27, Tomioka said. One of the bicyclists was transported to a hospital with non-life-threatening injuries, Tomioka said.

San Francisco Animal Care & Control officials responded and determined there was no mistreatment of the horse, according to Animal Care & Control Capt. Vicky Guldbech.

Guldbech concluded that there was nothing unusual about the horse and that signs of disturbance, neglect or abuse were not detected. She said it is possible the horse was simply having a bad night.

The horse was treated by a private veterinarian and returned to its stables in Petaluma, according to Guldbech.

"This incident should be a wake-up call for the city, and we urge officials to ban these rides before the next accident occurs," PETA director Debbie Leahy said in a statement.

PETA sent a letter to Newsom urging a ban of horse-drawn carriages, which have already been implemented in Biloxi, Miss.; Reno, Nev.; Palm Beach, Panama City, Key West, Deerfield Beach and Pompano Beach, Fla.; Santa Fe, N.M.; and Camden, N.J. There are also bans in London, Paris, Beijing and Toronto.